Graduate Thesis Or Dissertation
 

Theoretical influence of untransposed transmission line construction on system losses and voltage balance

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  • The purpose of this thesis is to investigate the necessity of transposition in the construction of overhead transmission lines. Line currents, line voltages and line losses of both the transposed and untransposed lines were calculated and compared for two different voltage classes. The conventional method of symmetrical components was used to determine both the negative- and zero-sequence currents produced by the inductive and capacitive unbalance in the untransposed lines. Both system voltages and line currents are affected when a transmission line is not transposed. This is a result of the two phenomena, (1) electromagnetic fields, and (2) electrostatic fields. To account for these effects, the transmission was modeled with a nominal-T network. The conductor configuration represented a single circuit, three-phase, three conductor system with a flat horizontal spacing. Shielding was represented by two ground-wire conductors. The necessary iterative calculations were performed on a digital computer. The unbalance generated by 100 miles of unbalanced line at a nominal voltage of either 230 Kv or 500 Kv did not produce an unbalance factor that exceeded the limits imposed by electrical machinery operation. The major effect of line unbalance is the influence of zero-sequence quantities on relaying systems and the additional power loss of the transmission lines. Both of these are functions of the length of the untransposed line. The calculated unbalance factors for 100 miles of untransposed lines are 0.0474 and 0.0626 for the 230 Kv and 500 Kv lines respectively. The above factors include the effect of the terminating equipment, transformers and equivalent machinery. Curves are presented to illustrate the phase currents, phase voltage drops, and the difference in transmission line power losses as functions of the length of the transposed and untransposed lines, for each voltage level.
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file details ChanakornChavalit1974__2_.pdf 2017-08-17 Öffentlich Herunterladen